Antimony thioantimonate and intermediate preparation for lubricant additive

ABSTRACT

Method of preparing alkali metal or ammonium thioantimonate and use of the thioantimonate in the preparation of SbSbS 4 , having a low level of free sulfur, and lubricants incorporating the SbSbS 4  as an additive.

BACKGROUND OF THE INVENTION

Antimony thioantimonate (SbSbS₄) has been prepared by reaction ofantimony oxide (dissolved in conc. potassium hydroxide solution) withsodium thioantimonate (Na₃ SbS₄) in an aqueous medium followed byneutralization of the resulting solution with an acid. See, for example,J. P. King and Yayesh Asmerom, "Investigation of Extreme-Pressure andAntiwear Properties of Antimony Thioantimonate", ASLE Transaction, Vol.24, 4, 497-504 (1981); and U.S. Pat. No. 3,965,016, to Soulen (issuedJune 22, 1976). The overall reaction can be written as follows: ##STR1##There are severe limitations associated with the above reaction, i.e.,(1) co-precipitation of free sulfur (6%) with the final product and (2)generation of hydrogen sulfide during neutralization. Subsequent studieshave shown that a side reaction simultaneously occurs during theneutralization step, as follows:

    2Na.sub.3 SbS.sub.4 +6H.sup.+ →SbSbS.sub.4 +3H.sub.2 S+S+6Na.sup.+( 2)

Excessive amounts (more than about 1%) of free sulfur in lubricantadditives (such as SbSbS₄ and others) are highly undesirable because thefree sulfur promotes corrosion of copper-containing metal parts. Becauseof the added costs in removing free sulfur from the final product andcollecting H₂ S, an improved and economic manufacturing process forpreparing SbSbS₄ is highly desirable.

This invention involves a modified reaction route with straight-forwardprocessing conditions to prepare SbSbS₄ having a low sulfur content. Thenew process can produce SbSbS₄ containing free sulfur at the moreacceptable level of about 1% or less. Furthermore, generation of H₂ Sduring neutralization is virtually eliminated. In addition, the newprocess does not require isolation and purification of the intermediate,Na₃ SbS₄.8H₂ O. A distinct advantage of the modified reaction route isthe fact that the second reaction (Equation 4) is simple and easilycontrolled. ##STR2##

By carefully controlling the reaction temperatures and pH of thereaction medium good yields of SbSbS₄ containing less than 1% freesulfur can be achieved. The examples listed in Tables I, II and IIIclearly demonstrate the importance and criticality of the reactionconditions in relation to free sulfur generation and the yields ofSbSbS₄. The following descriptions for preparing Na₃ SbS₄ solutions andSbSbS₄ from SbF₃ and SbCl₃ are the preferred procedures.

BRIEF SUMMARY OF THE INVENTION

The method of the invention for preparing the thioantimonateintermediate is defined as the method of preparing alkali metal orammonium thioantimonate without the formation of substantialby-products, comprising:

(a) forming an aqueous reaction mixture of

(i) sulfur,

(ii) a sulfide or hydrosulfide of an alkali metal or ammonium ion, ormixtures of said sulfides or hydrosulfides, and

(iii) a 1% to 10% molar excess of Sb₂ S₃ ; and

(b) maintaining the reaction mixture of (a) at a temperature within therange of from about 70° C. to about 105° C. for a sufficient period oftime to provide the alkali metal or ammonium thioantimonate without theformation of substantial by-products.

Preferably in (a) the molar excess of Sb₂ S₃ is within the range of 1.5to 5%.

The method of the invention for preparing low sulfur SbSbS₄ is definedas adding ammonium thioantimonate to a solution of SbX₃, wherein X is ahalide ion, to form a reaction medium while maintaining controlledreaction conditions, to provide a SbSbS₄ prduct having a low level offree sulfur impurity.

Preferably, the alkali metal or ammonium thioantimonate is added to thesolution of SbX₃ at a sufficiently slow rate to maintain substantiallyall the SbSbS₄ product in a solid phase. It is also preferred that theSbX₃ solution include as a solvent water or an alcohol of one to fourcarbon atoms or a mixture thereof, X be Cl⁻, and the intermediate be Na₃SbS₄. Preferably, the reaction medium is agitated during the addition ofalkali metal or ammonium thioantimonate, the method is a batch method,the reaction temperature is maintained during the addition of alkalimetal or ammonium thioantimonate within the range of 0° to 30° C., andthe pH of the reaction medium is maintained at substantially all timesduring the addition of alkali metal or ammonium thioantimonate at alevel of 7 or less (preferably by controlling the rate of addition ofthe alkali metal or ammonium thioantimonate to the SbX₃ solution).

The invention also includes lubricant compositions incorporating theSbSbS₄ of the invention as a lubricant additive.

DETAILED DESCRIPTION OF THE INVENTION Examples 1-6

Preparation of Sodium Thioantimonate Solutions:

In a typical reaction of the invention for preparing Na₂ SbS₄ (or thepotassium or ammonium salts) solution (Equation 3 above), a two-literround bottom flask fitted with a heating mantle, an electric motordriven stirrer, a water-cooled condenser, a thermometer and a nitrogeninlet and outlet tubes was used. The flask was first charged with 400ml. of distilled water followed by Sb₂ S₃ and sulfur with goodagitation. The reaction mixture was heated to 80° C. for three to fourhours. The resulting black slurry was then filtered and the blackresidue, NaSb(OH)₆, was washed with small amounts of distilled water andthe washings combined with the filtrate. The filtrate containing Na₃SbS₄ varied in color from light yellow to dark green. At times thefiltrate appeared black or lime colored. By using a slight excess (2%)of Sb₂ S₃, significant reduction of the by-product (black residue) wasachieved. Experimental results are recorded in Table I below.

                                      TABLE I                                     __________________________________________________________________________    Preparation of Na.sub.3 SbS.sub.4 Solution from Na.sub.2 S 9H.sub.2 O,        Sb.sub.2 S.sub.3, and S                                                                                       Vol. of                                                                             Weight of                               Dist.   Charge        Temp. of                                                                           Time of                                                                            Filtrate                                                                            Insoluble                               Example                                                                            H.sub.2 O                                                                        Na.sub.2 S.9H.sub.2 O                                                               Sb.sub.2 S.sub.3                                                                  S   Reaction                                                                           Reaction                                                                           Na.sub.3 SbS.sub.4                                                                  Residue                                 No.  ml grams grams                                                                             grams                                                                             °C.                                                                         hrs  sol'n, ml                                                                           grams Remarks                           __________________________________________________________________________    1    400                                                                              174.3 82.1                                                                              15.2                                                                               98-101                                                                            3.0  600   22.1  stoichiometric                    2    400                                                                              174.3 82.1                                                                              15.2                                                                              75-85                                                                              3.5  627   19.7  stoichiometric                    3    400                                                                              197.0 82.1                                                                              17.5                                                                              80-82                                                                              3.5  670   14.0  15% excess                                                                    Na.sub.2 S.9H.sub.2 O and S       4    400                                                                              174.3 90.4                                                                              15.2                                                                              79-84                                                                              3.5  640   14.9  10% excess Sb.sub.2 S.sub.3       5    400                                                                              174.3 83.8                                                                              15.2                                                                              79-85                                                                              3.5  637    3.7  2% excess Sb.sub.2 S.sub.3        6    400                                                                              174.3 83.8                                                                              15.2                                                                              81-84                                                                              3.5  620    1.4  2% excess Sb.sub.2 S.sub.3        __________________________________________________________________________

Examples 7-18

Preparation of SbSbS₄ from SbF₃ :

Thirty-five ml. of anhydrous ethanol were added to a 500 ml. roundbottom three-necked flask equipped with an electric motor drivenstirrer, a water-cooled condenser, a thermometer, an addition funnel anda nitrogen gas inlet and outlet. The alcohol was chilled to about 0° C.with an ice-salt bath under nitrogen atmosphere with stirring. Othersolvents such as H₂ O, CH₃ OH or isopropyl alcohol may also be used.Then 17.9 grams (0.1 mole) of SbF₃ were added. A cloudy solutionresulted. Then, the freshly filtered Na₃ SbS₄ solution was slowly added(over a 1 to 2 hour period), checking the pH at suitable intervals.Occasionally a pH of 8 was reached which would go to a lower pH after 20to 30 minutes of stirring. When a stable pH of 6 was observed, theaddition of Na₃ SbS₄ was stopped. This point usually corresponded toless than the theoretical amount of Na₃ SbS₄. The red slurry was heatedto reflux for two hours (the pH was again checked), filtered hot and thered cake washed three times with 300 ml. portions of hot-distilledwater, repulping each time and heating the repulped mixture to 75° C. to84° C. The red cake was then dried to constant weight in a 100° C. oven.Experimental data are recorded in Table II below.

                                      TABLE II                                    __________________________________________________________________________    Preparation of SbSbS.sub.4 from Na.sub.3 SbS.sub.4 and SbF.sub.3              Ex-                Na.sub.3 SbS.sub.4                                                                          pH at end    SbSbS.sub.4                     am-                                                                              SbF.sub.3       Solution Added                                                                        Temp. of                                                                            point of                                                                           Reflux                                                                            pH  Recov-                                                                            % Yield   % S.sup.o         ple                                                                              Charged                                                                            Sol-                                                                              Vol                                                                              Temp.                                                                             Vol..sup.1                                                                        % of.sup.2                                                                        Reaction                                                                             Na.sub.3 SbS.sub.4                                                                Time                                                                              after                                                                             ery Based                                                                              Based                                                                              Con-              No.                                                                              grams                                                                              vent                                                                              ml °C.                                                                        ml  Theory                                                                            °C.                                                                          add'n                                                                              hr  Reflux                                                                            grams                                                                             SbF.sub.3                                                                          Sb.sub.2 S.sub.3                                                                   tent              __________________________________________________________________________     7 17.9 H.sub.2 O                                                                         25 23  185 119  4 to 8                                                                             8    none                                                                              --  39.9                                                                              107  88   7.4                8 17.9 H.sub.2 O                                                                         25 24  .sup. 190.sup.5                                                                   124 -2 to 3                                                                             7    2   7   37.8                                                                              102  82   3.4                9 17.9 EtOH                                                                              25 26-7                                                                              190 130 -2 to 4                                                                             7    2   7   .sup. 37.3.sup.3                                                                  100  77   1.1               10 17.9 EtOH                                                                              25 0   160 113  2 to 6                                                                             7    2   7   .sup. 37.1.sup.4                                                                  100  86   0.8               11 17.9 EtOH                                                                              25 0   165 116 -1.4 to 8                                                                           7    2   6-7 37.1                                                                              100  84   1.8               12 17.9 EtOH                                                                              35 0   125 93  -1 to 4                                                                             6    2   6   34.3                                                                              92   105  1.1               13 17.9 EtOH                                                                              35 0   115 86  -1 to 6                                                                             6    2   6   31.3                                                                              84   95   0.95              14 17.9 EtOH                                                                              35 0   105 78  -2 to 1                                                                             6    2   5-6 28.8                                                                              77   95   0.90              15 17.9 EtOH                                                                              35 0   130 97  -2 to 5                                                                             6    2   6   35.6                                                                              96   95   1.2               16 17.9 EtOH                                                                              35 0   105 93   2 to 6                                                                             6-7  2   6   28.9                                                                              93   96   1.2               17 17.9 EtOH                                                                              35 0   110 84  -1 to 4                                                                             7    2   6   31.8                                                                              85   98   0.9               18 17.9 EtOH                                                                              35 0   110 81  -4 to 6                                                                             7    Stir 2                                                                            6   27.1                                                                              73   60   1.7                                                     hr at                                                                         r.t.                                    __________________________________________________________________________     .sup.1 This is the amount of Na.sub.3 SbS.sub.4 solution required to          produce the desired pH.                                                       .sup.2 It is assumed that the yield of Na.sub.3 SbS.sub.4 in the first        reaction is 100%. Since the second reaction is monitored by the pH            reading, the values in this column have no significant meaning but were       used as a rough guide while carrying out the second reaction.                 .sup.3 Total sulfur found in the product = 31.2% (theory, 33.2%). Fluorid     ion impurity found: 80 ppm.                                                   .sup.4 Total sulfur found in the product = 33.1% (theory, 33.2%). Fluorid     ion impurity found: 110 ppm.                                                  .sup.5 64 ml. added initially which caused pH to go above 7 and produce       high free sulfur.                                                        

Examples 20-24

Preparation of SbSbS₄ from SbCl₃ :

Twenty-five ml. of anhydrous ethanol were added to a 500 ml. roundbottom three-necked flask equipped with an electric motor drivenstirrer, a water-cooled condenser, a thermometer, an addition funnel,and a nitrogen gas inlet and outlet. The alcohol was chilled to around0° C. with an ice-salt bath under a nitrogen atmosphere, with stirring.Then, 22.8 grams (0.1 mole) of SbCl₃ were added. A slightly cloudysolution resulted. Then, the freshly filtered Na₃ SbS₄ solution wasslowly added, checking the pH at suitable intervals. When a stable pH of6 was observed, the addition of Na₃ SbS₄ was stopped. The resulting redslurry was heated to reflux for two hours (the pH was again checked),filtered hot and washed three times with 300 ml. portions of hotdistilled water, repulping each time and heating the repulped mixture to75° C. to 85° C. The red cake was dried to constant weight in a 100° C.oven. The results are given in Table III below.

                                      TABLE III                                   __________________________________________________________________________    Preparation of SbSbS.sub.4 from Na.sub.3 SbS.sub.4 and SbCl.sub.3             Ex-                    Na.sub.3 SbS.sub.4                                                                          pH at end                                                                          Re-                                                                              pH SbSbS.sub.4                                                                       % Yield                   am-                                                                              SbCl.sub.3          Solution Added                                                                        Temp. of                                                                            point of                                                                           flux                                                                             after                                                                            Recov-                                                                            Based                                                                             Based                                                                             % S.sup.o         ple                                                                              Charged     Vol Temp.                                                                             Vol..sup.1                                                                        % of.sup.2                                                                        Reaction                                                                            Na.sub.3 SbS.sub.4                                                                 Time                                                                             Re-                                                                              ery on  on  Con-              No.                                                                              grams                                                                              Solvent                                                                              ml  °C.                                                                        ml  Theory                                                                            °C.                                                                          add'n                                                                              hr flux                                                                             grams                                                                             SbCl.sub.3                                                                        Sb.sub.2 S.sub.3                                                                  tent              __________________________________________________________________________    20 22.8 H.sub.2 /conc HCl                                                                     26/9.8                                                                           25  175 141 -2.5 to 8                                                                            none                                                                              none                                                                             -- 41.0                                                                              110 80  2.0               21 11.4 EtOH   25  25   94 111 -4 to 7                                                                             5    none                                                                             -- 18.9                                                                              102 93  1.3               22 11.4 H.sub.2 O/EtOH                                                                       1.2/0.5                                                                           25   94 111 -2 to 3                                                                             7    none                                                                             -- 17.8                                                                               96 87  1.4               23 41.9 EtOH   46  26  289 120  2 to 6                                                                             7    none                                                                             -- 68.4                                                                              108 83  1.7               24 22.8 EtOH   25   0  130 102 0-7   6    2  5  37.1                                                                              100 96  2.0               __________________________________________________________________________     .sup.1 This is the amount of Na.sub.3 SbS.sub.4 solution required to          produce the desired pH.                                                       .sup.2 It is assumed that the yield of Na.sub.3 SbS.sub.4 in the first        reaction is 100%. Since the second reaction is monitored by the pH            reading, the values in this column have no significant meaning but were       used as a rough guide while carrying out the second reaction.            

Example 25

Effect of Addition Time of Sodium Thioantimonate Solution to AntimonyTrihalide Solution on Free Sulfur Content in the Preparation of SbSbS₄ :

An aqueous solution of 0.10M of sodium thioantimonate (Na₃ SbS₄) wasprepared using 2% excess of antimony trisulfide (Sb₂ S₃) according tothe procedure described for the preparation of sodium thioantimonatesolution previously described. The sodium thioantimonate solution wasdivided equally into two parts which were then used to ascertain whetherfast or slow addition of Na₃ SbS₄ solution to alcoholic antimonytrifluoride (SbF₃) solution in the preparation of SbSbS₄ has any effecton free sulfur content in the final products.

For the fast addition experiment, a sample of 8.59 g. (0.05M) of SbF₃was dissolved in 17.5 ml. 200 proof ethanol in a 500 ml. flask which wasimmersed in a water bath at 17° C. and equipped with a reflux condenser,mechanical stirrer, addition funnel, N₂ inlet and outlet. One-half ofthe Na₃ SbS₄ solution prepared above was added fairly rapidly at arelatively constant rate (33 minutes) to the alcoholic SbF₃ solution,with constant agitation. The pH of the reaction mixture was 6 throughoutmost of the addition period. A pH value of 8 was observed upon completeaddition of the Na₃ SbS₄ solution; however, it changed back to pH 6after 30 minutes of agitation. The reaction mixture was allowed toagitate for one hour at about 18° C. and was filtered. The wet SbSbS₄was washed repeatedly three times with hot distilled water (85° C.). Thesolid product was dried in a 100° C. oven overnight and weighed 32.0 g.(86.5% yield). The free sulfur content in the dry SbSbS₄ was found to be2.22%.

For the slow addition experiment, the other half of the Na₃ SbS₄solution was reacted with 8.95 g. of SbF₃, dissolved in 17.5 ml. 200proof ethanol under the same conditions as described above, with theexception of addition time. In the latter case, the addition time was120 minutes instead of 33 minutes as in the fast addition experiment.The pH remained at 7 or less throughout the experiment. The overallyield was 86% and the free sulfur content in the dry SbSbS₄ product wasfound to be 0.53%. By keeping the other experimental parametersconstant, if has been shown that maintenance of the pH at 7 or less byslow addition of Na₃ SbS₄ solution to an alcoholic SbF₃ solution willresult in lower free sulfur content in the final SbSbS₄ product.

We claim:
 1. Method of preparing alkali metal or ammonium thioantimonatewithout the formation of substantial by-products, comprising:(a) formingan aqueous reaction mixture of(i) sulfur, (ii) a sulfide or hydrosulfideof an alkali metal or ammonium ion, or mixtures of said sulfides orhydrosulfides, and (iii) a 1% to 10% molar excess of Sb₂ S₃ ; and (b)maintaining the reaction mixture of (a) at a temperature within therange of from about 70° C. to about 105° C. for a significant period oftime to provide the alkali metal or ammonium thioantimonate without theformation of substantial by-products.
 2. The method as in claim 1wherein in (a) the molar excess of Sb₂ S₃ is within the range of 1.5 to5%.
 3. The method as in claim 1 wherein in (b) the temperature is withinthe range of 75° C. to 100° C.
 4. The method as in claim 1 wherein thesulfide or hydrosulfide is hydrated.
 5. The method as in claim 1 whereinthe alkali metal or ammonium thioantimonate of 1(b) is then added to asolution of SbX₃, wherein X is a halide ion, to form a reaction mediumwhile maintaining controlled reaction conditions, to provide a SbSbS₄product having a low level of free sulfur impurity.
 6. The method as inclaim 5 wherein the alkali metal or ammonium thioantimonate is added tothe solution of SbX₃ at a sufficiently slow rate to maintainsubstantially all the SbSbS₄ product in a solid phase.
 7. The method asin claim 6 wherein the SbX₃ solution includes as a solvent water or analcohol of one to four carbon atoms or a mixture thereof.
 8. The methodas in claim 7 wherein X is Cl⁻ and the alkali metal or ammoniumthioantimonate is Na₃ SbS₄.
 9. The method as in claim 8 wherein thereaction medium is agitated during the addition of alkali metal orammonium thioantimonate.
 10. The method as in claim 5, 6, 7, 8 or 9wherein the method is a batch method.
 11. The method as in claim 5, 6,7, 8, or 9 wherein the reaction temperature is maintained during theaddition of alkali metal or ammonium thioantimonate within the range of0° to 30° C.
 12. The method as in claim 5, 6, 7, 8 or 9 wherein the pHof the reaction medium is maintained at substantially all times duringthe addition of alkali metal or ammonium thioantimonate at a level of 7or less.
 13. The method of claim 12 wherein the pH of 7 or less ismaintained by controlling the rate of addition of the alkali metal orammonium thioantimonate to the SbX₃ solution.
 14. The method of claim 12wherein the method is a batch method.
 15. The method of claim 12 whereinthe reaction temperature is maintained during the addition of alkalimetal or ammonium thioantimonate within the range of 0° to 30° C. 16.Method of preparing SbSbS₄ product having a low level of free sulfurimpurity, comprising: adding an alkali metal or ammonium thioantimonateintermediate to a solution of SbX₃, wherein X is a halide ion, to form areaction medium while maintaining controlled reaction conditions inwhich the alkali metal or ammonium thioantimonate intermediate is addedto the solution of SbX₃ at a sufficiently slow rate with agitation ofthe reaction medium to maintain substantially all the SbSbS₄ product ina solid phase, to provide a SbSbS₄ product having a low level of freesulfur impurity.
 17. The method as in claim 16 wherein the SbX₃ solutionincludes as a solvent water or an alcohol of one to four carbon atoms ora mixture thereof.
 18. The method as in claim 17 wherein X is Cl⁻ or F⁻.19. The method as in claim 18 wherein the reaction medium is agitatedduring the addition of alkali metal or ammonium thioantimonate.
 20. Themethod as in claim 16, 17, 18 or 19 wherein the method is a batchmethod.
 21. The method as in claim 16, 17, 18 or 19 wherein the reactiontemperature is maintained during the addition of alkali metal orammonium thioantimonate within the range of 0° to 30° C.
 22. The methodas in claim 16, 17, 18 or 19 wherein the pH of the reaction medium ismaintained at substantially all times at a level of 7 or less.
 23. Themethod of claim 22 wherein the pH of 7 or less is maintained bycontrolling the rate of addition of the alkali metal or ammoniumthioantimonate to the SbX₃ solution.
 24. The method of claim 22 whereinthe method is a batch method.
 25. The method of claim 22 wherein thereaction temperature is maintained during the addition of alkali metalor ammonium thioantiomonate within the range of 0° to 30° C.
 26. Themethod as in claim 16, 17, 18, or 19 wherein after the addition of thealkali metal or ammonium thioantimonate the reaction medium containingthe SbSbS₄ product is heated to a temperature within the range of 80° C.to about 100° C. for a sufficient period of time to assure substantiallycomplete reaction of the reactants in the reaction medium.
 27. Themethod of claim 26 wherein the period of time is less than about twohours.